JPH01120137A - Optical receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coherent detection optical receiver for wavelength multiplexed optical communication.

[Conventional technology]

Conventionally, an optical receiver for a wavelength multiplexed optical signal has an I2
European Conference on Optical Communication Technical Digest
Volume III (1986) pp. 29-32
Page (12th European conference
eon Qptical Communication
Volume (1986) pp. 29-32).

[Problem that the invention seeks to solve]

When an optical signal propagates through a medium with dispersion, it is subject to delay distortion that depends on the signal wavelength and transmission distance.

Therefore, in a coherent detection optical receiver whose reception wavelength is variable, the received and detected electrical signal is subject to different delay distortions depending on the reception wavelength.The role of an equalizer is to correct delay distortion. However, if an equalizer is constructed by ignoring the delay distortion that differs for each wavelength, it will not be possible to completely compensate for all the delay distortions, resulting in deterioration of reception sensitivity.Furthermore, an adaptive automatic equalizer can be used to Even when dealing with delay distortion, the configuration becomes complicated.

An object of the present invention is to solve the above-mentioned deterioration of reception sensitivity or the complexity of the equalizer configuration.

[Means for solving problems]

The above object is achieved by using the wavelength information of the local light that determines the receiving wavelength and changing the isolator characteristics in order to correct delay distortion depending on the receiving wavelength.

[Operation] Figure 1 shows the conceptual causes of the receiver groove bottom. The figure shows a heterogain detection optical receiver that can select the received signal wavelength. 1 is a receiving wavelength selector, and 2 is a local light source.

3 is a beam splitter 44 is a photoelectric converter, 5 is an amplifier,
6 is an IF equalizer, 7 is an IF detector, 8 is a baseband equalizer, and 9 is a determiner.

The reception wavelength selector 1 controls the local light source 2 to determine the reception wavelength, and changes the characteristics of the IF equalizer 6 and the baseband equalizer 8 so as to correct wavelength-dependent delay distortion.

FIG. 1 shows the case of a heterodyne detection optical receiver. In the case of a homodyne optical receiver, the IF equalizer 6 and IF detector 7 in FIG. 1 are omitted.

The basic operation is the same.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to a receiver compatible with a wavelength division multiplexing optical transmission system in which each channel is assigned a different wavelength will be described with reference to FIG.

FIG. 2 is a block diagram of the front end and IF stage equalization amplification section of the heterodyne detection optical receiver. 10 is a reception channel selector, 11 is an equalizer for each channel, and 12 is a common equalizer. The IF equalizer 6 is composed of 11 and 12.

The receiving channel selector 10 generates a local laser 2 control signal and a channel-based equalizer 11 selection signal in response to a channel selection request from a user or other system. Here, the channel-specific equalizer 11 is adjusted in advance to correct delay distortion caused by the dispersion characteristics of the transmission path using the wavelength assigned to the channel. Original signal 'lt of selected channel
When received, the j5IF amplifier 5 converts the received optical signal into an electrical signal having the center frequency at the IF frequency and outputs it based on the principle of heterodyne detection. The output of the IF amplifier 5 is subjected to delay distortion that varies depending on the receiving wavelength. However, since the equalizer for each channel 11 corrects the delay distortion of 7, the input of the common equalizer 12 does not have delay distortion due to dispersion of the transmission path.

A receiver configured as shown in FIG. 2 is easier to implement than a receiver having an adaptive automatic equalizer designed to equalize delay distortion without information on the wavelength of received light.

Furthermore, compared to the case where an equalizer with fixed characteristics is used as the equalizer 6, deterioration in sensitivity due to delay distortion that varies depending on the wavelength does not occur.

Generally, an adaptive automatic equalizer is used for the common equalizer 12 in order to cope with distortion caused by causes other than dispersion of the transmission path medium, such as distortion caused by changes in transmitter characteristics. Sufficient characteristics can be obtained even with a fixed isolator.

The embodiment shown in Fig. 2 is an example in which the delay distortion due to the transmission path medium is equalized by 9 using only the IF equalizer, but as shown in Fig. 1, the IF
Equalization functions can also be distributed between an equalizer and a baseband equalizer.

The advantage of providing an individual equalizer 11 for each channel is that sufficient reception characteristics can be obtained by applying it to a system in which channel-specific distortion is caused by causes other than transmission line dispersion.

FIG. 3 shows an example in which the equalizer 6 is configured with a single equalizer instead of using a plurality of channel equalizers 11 as shown in FIG. 13 is a channel information table, 1
4 is a variable delay equalizer.

Delay distortion due to fiber dispersion is Δ”=　kcf-ft) f: frequency fi: intermediate frequency Δτ: relative delay time to fl k: delay coefficient It can be equalized by a delay equalizer with the following characteristics.

The reception channel selector 10 reads information on the wavelength corresponding to the reception channel, dispersion for the wavelength, and transmission distance from the channel information table 13. Then, according to the following equation, the delay coefficient k
i is calculated and the variable delay equalizer 14 is controlled.

k=,=tdλ2/(t: transmission distance d: dispersion λ: wavelength C: speed of light [Effects of the Invention] According to the present invention, delay distortion that varies depending on the receiving wavelength can be corrected without analyzing the received signal. Therefore, the construction of the automatic equalizer becomes easy.

Further, there is an effect that there is no deterioration in reception sensitivity due to incomplete correction of delay distortion that occurs in a receiver having the same equalizer characteristics for any wavelength.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the conceptual configuration of the present invention. FIG. 2 is a block diagram of one embodiment, and FIG. 3 is a block diagram of another embodiment. 1... Reception wavelength selector, 2... Local light source, 6...
・IF equalizer, 8...Baseband equalizer, 10...
- Reception channel selector, 11... channel-specific equalizer,
12... Common equalizer, 13... Channel information table, 14... Variable delay equalizer.

Claims (1)

[Scope of Claims] 1. A local light source having a variable wavelength of local light, and an equalizer that changes equalization characteristics based on wavelength information of the local light,
An optical receiver characterized in that the equalizer equalizes distortion due to dispersion of a transmission path that depends on the wavelength of received light. 2.Equipped with an equalizer consisting of a plurality of individually adjustable equalization circuits, each of which is adjusted to equalize distortion due to dispersion of each channel, and a channel selector changes the local light wavelength and changes the equalization circuit between channels. 2. The optical receiver according to claim 1, wherein the optical receiver switches to an equalization circuit corresponding to . 3. An equalizer having a delay characteristic proportional to frequency and a variable proportionality coefficient is provided, and the proportionality coefficient of the equalizer is changed in accordance with the wavelength of the local light. optical receiver. 4. Equipped with a channel information table that stores channel-specific information such as wavelength, dispersion at that wavelength, transmission distance, etc. When selecting a channel, the proportional coefficient of the equalizer is calculated from the information in the channel information table to determine the equalizer characteristics. The optical receiver according to claim 3, characterized in that the optical receiver changes: